Perform detailed analyses of the hemodynamic data collected as part of the Nocturnal Oxygen Therapy Trial. These analyses and any publications arising from them will serve to extend results presented in the NOTT Study Group paper (1980). Additional variables will be analyzed in a more extensive fashion on a data set that has been more carefully reviewed for invalid entries. The relationship between hemodynamic variables (both at baseline and changes over six months), survival, and selected clinical variables will be examined.